1. Field of the Invention
This invention relates to the conversion of sodium bicarbonate to a lower bulk density product containing at least 10% Wegscheider's Salt (Na.sub.2 CO.sub.3.3NaHCO.sub.3), by weight. The product is a soluble, low density, mildly alkaline base which absorbs liquid wetting agent without subsequent "bleeding" onto the packaging material. This product may be used in the preparation of laundry detergents containing substantially no phosphates.
2. Description of the Prior Art
The preparation of Wegscheider's Salt by heating aqueous sodium bicarbonate at temperatures ranging from about 75.degree. to 120.degree. C. is known. This concept is disclosed in U.S. Pat. Nos. 1,583,660 and 1,583,662 and in British Pat. No. 202,678. British Pat. No. 202,678 discloses that at 98.degree. C. substantially full conversion was obtained in 11/2 hours, that at 95.degree. C. substantially full conversion was obtained in 6 hours and that at 90.degree. C. about 50% conversion was obtained in 11 hours. Processes for heating wet sodium bicarbonate alone as described in these patents are not now commercially feasible. Product material tends to stick and cake, and a satisfactory low density product suitable for use as a detergent is not obtainable.
Dry sodium bicarbonate is known to decompose very slowly to Wegscheider's Salt. For example, dry crude sodium bicarbonate, when heated to about 120.degree. C. for about 50 minutes, contained only about 5% Wegscheider's Salt; on the other hand, wet crude sodium bicarbonate heated to about 120.degree. C. for about 50 minutes formed 50% Wegscheider's Salt in 50 minutes.
Addition of sodium carbonate to aqueous sodium bicarbonate is disclosed in U.S. Pat. Nos. 1,473,259 and 1,583,662 and British Pat. No. 210,628. These patents disclose that about 30% (dry basis) or about 28-29% (wet basis) sodium carbonate by weight, is present in the feed. Such addition of sodium carbonate, per se, tends to reduce the sticking and caking problem and to increase reaction rate but does not result in products having low bulk densities, e.g. as low as about 95 grams per liter, for high Wegscheider's Salt values, i.e. in excess of 50% Wegscheider's Salt in the product.